Genetic elements novel for Corynebacterium diphtheriae: specialized transducing elements and transposons

Conjugative Plasmid in Corynebacterium flaccumfaciens subsp. oortii That Confers Resistance to Arsenite, Arsenate, and Antimony(III)

Gene transfer systems for phytopathogenic corynebacteria have not been reported previously. In this paper we describe a conjugative 46-megadalton plasmid (pDG101) found in Corynebacterium flaccumfaciens subsp. oortii CO101 that mediates resistance to arsenite, arsenate, and antimony(III). Transfer of the plasmid from CO101 to four other strains from the C. flaccumfaciens group occurred between cells immobilized on nitrocellulose filters or on agar surfaces. Transconjugant strains expressed the same levels of metal resistance as the donor strain and were able to act as donor strains in subsequent matings. The physical presence of the plasmid was detected by agarose gel electrophoresis. Arsenite-sensitive derivatives of the donor and transconjugant strains were obtained after heat treatment; these were cured of pDG101.

Characterization of bacteriophages from tox-containing, non-toxigenic isolates of Corynebacterium diphtheriae

Non-toxigenic strains of Corynebacterium diphtheriae continue to cause disease within immunized populations. A subset of these corynebacteria carry the diphtheria toxin gene but in a cryptic form. To determine whether such strains might contribute to the re-emergence of functional toxin genes, the phages and tox mutations within three clone types were examined. tox-containing, beta-related phages were isolated from two of the strain types. The third isolate appeared to harbour a defective prophage. One of the tox- phages encoded truncated, yet enzymatically-active, forms of diphtheria toxin, suggesting that it had sustained a point mutation within the latter half of its toxin gene. In contrast, the other mutant phage did not elicit the production of either a cross-reacting material or an ADP-ribosylating activity. Complementation tests employing a series of double lysogens confirmed that the mutations responsible for the non-toxigenic phenotype of all of the phages were cis dominant. Given these findings, it is reasonable to hypothesize that tox+ genes can arise within human populations by either homologous recombination between two distinct tox- phages or spontaneous reversion within a single mutant allele.

Pediatric immunizations

The record of disease prevention in children is an impressive testament to our universal immunization program. However, these successes are being threatened by rates of vaccination in some areas of the country that are substantially less than those seen in the developing world. Unless the pediatric immunization rates are improved, epidemics of other vaccine-preventable diseases will recur, as evidenced by the measles outbreaks. Although the tools needed for disease prevention are available, the means for their delivery are lacking. It is the obligation of us all to immunize the nation's children.

DNA element of Corynebacterium diphtheriae with properties of an insertion sequence and usefulness for epidemiological studies

The segment of DNA which is inserted within the tox gene of bacteriophage gamma and is responsible for its Tox- phenotype was found to be present and repeated approximately 30 times in the chromosome of Corynebacterium diphtheriae Belfanti 1030. Other C. diphtheriae strains contained a variable number of copies (1 to 25) of the same element. Sequence analysis showed that this repeated and interspersed DNA element was flanked by 9-base-pair direct repeats and that the 5' and 3' ends of the insertion contained sequences forming an imperfect inverted repeat. Therefore, the DNA segment here described has most of the typical structural features of a bacterial insertion sequence element. We show that different C. diphtheriae isolates derived from the same outbreak of diphtheria have an identical genomic distribution of this DNA element and that such DNA can be useful for epidemiological studies.

DNA relationships among some tox-bearing corynebacteriophages

The DNA genomes of a number of tox-bearing, temperate corynebacteriophages isolated from strains of Corynebacterium diphtheriae and Corynebacterium ulcerans were compared. With one exception, these phages displayed similarities in their restriction enzyme digest profiles and extensive homology with prototypic beta converting phage. The exception, phage delta, had a unique restriction profile and exhibited homology with beta over a limited portion of its genome. DNAs of phages from each host contained cohesive ends and integrated as prophage by a mechanism analogous to that employed by coliphage lambda. It is proposed that these tox-bearing phages belong to a common family, the beta family. The role of the beta family in the movement of the tox gene between strains of C. diphtheriae and C. ulcerans is discussed.

Characterization of the diphtheria tox transcript in Corynebacterium diphtheriae and Escherichia coli

Transcription of the tox gene in lysogenic Corynebacterium diphtheriae strains C7(beta tox+), C7 (gamma tox) and the hypertoxigenic PW8 (omega tox+) was analyzed and compared with transcription of the C. diphtheriae tox gene in the recombinant strain Escherichia coli (pDT201). In all cases S1 nuclease mapping localized the 5' terminus of the tox mRNA to a site 8 or 9 base pairs (bp) downstream of a region similar to the -10 consensus sequence of E. coli promoters. In C. diphtheriae the tox transcript was observed only in strains that were grown under iron-limiting conditions; in the presence of excess iron, transcription beyond bp 38 of the tox coding region was not observed. In contrast, in E. coli(pDT201) tox was expressed at equivalent levels in both iron-depleted and iron-supplemented media. The DNA insertion in the tox gene of the nontoxigenic corynephage gamma was found to occur at bp 54 of the tox coding region. The insertion event resulted in the duplication of a 7-bp target sequence, and the ends of the insert were found to constitute an imperfect inverted repeat of approximately 26 bp. Transcription from the tox promoter in C7(gamma tox) was found to initiate at the same nucleotides as in C7(beta tox+), PW8, and E. coli(pDT201) and remained sensitive to iron inhibition. These observations are discussed in relation to the mechanism of iron-mediated regulation of the tox gene.

Detection and physical map of a omega tox+-related defective prophage in Corynebacterium diphtheriae Belfanti 1030(-)tox-

A library of chromosomal DNA from Corynebacterium diphtheriae Belfanti 1030(-)tox- was cloned in the lambda phage vector EMBL4 and screened for sequences homologous to corynephage omega tox+ and the attB1-attB2 region of the C7(-)tox- chromosome. Two portions of the 1030(-)tox- chromosome, 35 and 30.5 kilobases long which contain, respectively, the entire region homologous to corynephage omega tox+ and the attB1-attB2 sites, were mapped with the restriction endonucleases BamHI and EcoRI. Chromosomal DNA from 1030(-)tox- was shown to contain a 15.5-kilobase region that was homologous to ca. 42% of the corynephage omega tox+ genome. These sequences were found to hybridize to three regions of the phage genome and do not contain either the diphtheria tox operon or the attP site. These sequences are distant from the chromosomal region that contains the attB1-attB2 sites. Moreover, unlike other known defective prophages, the physical map of this prophage starts at the cos site and is colinear with the vegetative phage map. The 30.5-kilobase region of the 1030(-)tox- chromosome, which contains the attB1-attB2 sites, has a central core region that is almost identical to the corresponding region of the C7(-)tox- chromosome; however, the flanking sequences in these two strains of C. diphtheriae are different.

Conversion by corynephages and its role in the natural history of diphtheria

The conversion of non-toxinogenic Corynebacterium diphtheriae to toxinogeny has been reviewed. The biology of converting phage and the relationship of converting phages to nonconverting phages are summarized. The significance of these findings to the natural history and evolution of diphtheria is assessed.

Physical map of the chromosomal region of Corynebacterium diphtheriae containing corynephage attachment sites attB1 and attB2

The chromosome of Corynebacterium diphtheriae C7 was recently shown to contain two equivalent attachment sites (attB1 and attB2) for lysogenization by corynephages (R. Rappuoli, J.L. Michel, and J.R. Murphy, J. Bacteriol. 153:1202-1210, 1983). Portions of bacterial chromosome containing each attB site, as well as a 3.5-kilobase (kb) EcoRI fragment containing both attB1 and attB2 sites, were cloned in the pUC8 plasmid vector. Restriction endonuclease mapping and Southern blot hybridization analysis of restriction endonuclease fragments showed that attB1 and attB2 are 2.25 kb apart on the chromosome. Furthermore, a 0.85-kb HincII-EcoRI restriction endonuclease fragment containing attB1, a 0.77-kb HincII-BamHI fragment containing attB2, and a 1.2-kb EcoRI-BamHI fragment containing attP share short homologous regions. No homology was detected between the sequences flanking the two attB sites. The isolation of a segregant which had lost the entire chromosomal segment contained between attB1 and attB2 suggests that this region is not essential for growth.

Restriction endonuclease map of the nontoxigenic corynephage gamma c and its relationship to the toxigenic corynephage beta c

Clear-plaque-forming mutant gamma tox- corynephages were isolated independently from nontoxigenic lysogenic Corynebacterium diphtheriae strains C7s(gamma tox-) and C4(gamma tox-). A physical map was constructed by using restriction endonucleases BamHI, EcoRI, HindIII, and KpnI. A comparison of nontoxigenic gamma c with toxigenic corynephage beta c revealed large areas of homology, including common regions for cohesive ends (cos) and attachment sites (att). Localization of the att sites on the beta prophage and correlation of the physical and genetic maps defined the orientation of the diphtheria tox operon. Diphtheria tox sequence homologies were mapped on gamma c by hybridizing 32P-labeled diphtheria tox mRNA to restriction fragments of gamma c DNA. Two regions of heterogeneity between phages beta c and gamma c were localized and these regions accounted for the 3-kilobase larger molecular size of gamma c compared with beta c. One change occurs near the tox promoter and may explain the nontoxigenic phenotype of corynephage gamma tox-.

Physical mapping of beta-converting and gamma-nonconverting corynebacteriophage genomes

Deoxyribonucleic acids (DNAs) from wild-type and mutant strains of beta-converting and gamma-nonconverting corynebacteriophages were isolated and physically characterized. The data obtained from DNA heteroduplexes, restriction enzyme banding profiles, and restriction maps reinforce the conclusion that beta and gamma phages are very closely related. The major physical differences seen in the DNA heteroduplexes are a small substitution bubble and one or two insertions which are present on the gamma phage genome. The insertions account for the differences in the genome sizes of beta and gamma phages, and with the substitution they are responsible for most of the differences in the restriction endonuclease profiles and maps of the corynebactriophage genomes, two special sites and the DNA fragments carrying them were identified. These were the cohesive (cos) sites and the specific attachment (attP) site of the vegetative phage genome. The behavior of these sites indicated that the transition of phage DNA from the vegetative to the prophage state involves the circularization of vegetative DNA through the cos sites and its integration into the bacterial chromosome via the attP site. The mechanism of corynebacteriophage integration was similar to that employed by Escherichia coli phage gamma. From the data assembled the physical and genetic maps of beta and gamma phage were oriented with respect to one another. The extensive similarity in their maps provides additional confirmation of a close evolutionary relationship.

Identification of deoxyribonucleic acid restriction fragments of beta-converting corynebacteriophages that carry the gene for diphtheria toxin

Deoxyribonucleic acid fragments bearing the gene for diphtheria toxin have been identified in restriction enzyme digests of deoxyribonucleic acids from beta-converting and gamma-nonconverting corynebacteriophages. A combination of physical and genetic evidence has established that the Bam HI band C fragment of beta phage deoxyribonucleic acid, which carries the specific phage attachment site (Buck and Groman, J. Bacteriol. 148:131-142, 1981), also carries most, and probably all, of the gene for diphtheria toxin. A detailed restriction map of this tox-bearing Bam HI fragment has been developed, and the locations and orientation of the tox gene and the attP site within this fragment have been established.